In a fuel cell, electrical energy and heat are generated by the combination of hydrogen (H2) and oxygen (O2) in an electrochemical reaction, the hydrogen and the oxygen being combined to form water (H2O). A single fuel cell supplies an operating voltage of a maximum of 1.1 V. For this reason, a plurality of planar fuel cells are stacked one on top of the other and are combined to form a fuel cell block. By virtue of the fuel cells of the fuel cell block being connected in series it is possible for the operating voltage of the fuel cell block to be several hundred volts. A fuel cell in a fuel cell block includes a diaphragm electrode unit which is also referred to as an electrolyte electrode unit, and the composite printed circuit board which is adjacent thereto on both sides. The composite printed circuit board can be configured as cooling elements.
The technical implementation of the principle of the fuel cell has lead to different solutions, specifically with different types of electrolytes and operating temperatures between 80° C. and 1000° C. Depending on its operating temperature, the fuel cells are classified as low-temperature fuel cells, medium-temperature fuel cells and high-temperature fuel cells which are distinguished in turn by various technical embodiments.
The heat which is produced in a fuel cell by the electrochemical reaction must be carried away from the fuel cell so that the fuel cell is not destroyed by overheating. In the case of a low-temperature fuel cell, this heat is usually carried away using a coolant circuit, the coolant, generally water, flowing through the fuel cell, absorbing heat there and giving off the heat outside the fuel cell. For this purpose, the fuel cell includes a cooling element which can be used either for cooling the fuel cell or else for heating the fuel cell, for example when the fuel cell block is started up. The coolant element has a coolant space through which the coolant, generally the cooling water, flows while the fuel cell is operating. The coolant space has a coolant inflow and a coolant outflow, the coolant inflow and the coolant outflow being arranged in such a way that the stream of coolant which flows from the inflow to the outflow cools the fuel cell as uniformly as possible.
EP 0 591 800 B1 discloses a cooling element which is composed of two plates and has a rectangular coolant space, the inflow and the outflow for the coolant being arranged in corner regions of the coolant space which are diagonally opposite one another. When cooling water flows through such a coolant space, the centre region of the coolant space is effectively cooled, but only a small amount of cooling water flows through the corner regions of the coolant space which are not adjacent to the inflow or outflow. This results in the fuel cell being heated to a greater degree in these corner regions than in its central region which adjoins the central region of the coolant space. In an extreme case, such defective conveying away of heat from the corner regions through which there is a weak flow leads to the electrolyte diaphragm of the fuel cell being destroyed at these points.